During a planting time of corn, etc., a triazine-based herbicide such as atrazine and acid anilide-based herbicides such as alachlor and metolachlor have been mainly used. However, these herbicides are causing environmental problems such as the pollution of ground water, etc., due to their high dosage requirement.
Further, it is a known fact that when herbicides of specific series are used for a long period of time, some weeds begin to exhibit resistance to the herbicides. Those weeds which are difficult to control, including the above resistant weeds, are becoming non-negligible. In view of this fact, herbicidal compounds having a novel skeleton and herbicidal compositions containing these compounds are still highly demanded.
Pyrazole-containing herbicides which can replace the above triazine-based herbicides and the above acid anilide-based herbicides are known, and those of the following formulae are commercially available. ##STR2##
However, the above compounds are both used as herbicides for paddy rice, and have been used during a planting time of field crops such as corn in no case.
International Laid-open Patent Publication No. WO93/18031 discloses a herbicidally active pyrazole derivative having a thiochroman ring. The typical compounds (A) and (B) thereof have structures as shown below. ##STR3##
The above compounds (A) and (B) exhibit good herbicidal efficacy both in post-emergence treatment. Especially compound (A) exhibits an excellent herbicidal efficacy on broad-leaved weeds in post-emergence treatment, while it shows insufficient efficacy on grass weeds. Further, compounds (A) and (B) show somewhat insufficient efficacy when used in pre-emergence treatment.
Further, International Laid-open Patent Publication No. WO95/04054 discloses herbicidally active pyrazole derivatives having a thiochroman ring, represented by the following general formula. ##STR4##
wherein each of X.sup.2 and X.sup.3 is a C.sub.1 .about.C.sub.4 alkyl group. The explanation of the other symbols is omitted.
The structures of the typical compounds (C) and (D) in the above International Laid-open Patent Publication are as shown below. ##STR5##
The above compound (D) exhibits sufficient herbicidal efficacy against several kinds of broad-leaved and grass weeds even when the treatment is carried out at an effective dose of as low as 100 g per hectare, while there are some weeds, some grass weeds in particular, against which its efficacy is insufficient when it is applied to a broader range of weeds.